WISN 12 News has learned that the U.S. Secret Service is tracking an international ring of thieves in Milwaukee, and the suspects are doing their work in a very public setting.

Officials with the Secret Service said the scheme has been in business for seven years, and they're committing their crimes in very public places.

WISN 12 News investigative reporter Colleen Henry learned of the investigation when the government filed subpoenas to track -- of all things -- library cards.

The thieves buy blocks of tickets using hacked credit card accounts, then resell copies of those tickets online.

When Florence and the Machine played at The Rave in Milwaukee last April, some concert-goers found out they were duped as the tickets they bought on Craigslist turned out to be duplicates of a single ticket. Officials said that is the motive of this international crime ring.

Gordon and Jan Thelin of Virginia bought tickets to the show, but had a surprise when they received their credit card bill.

"I remember looking at it and we were just like 'Wait a minute, we did not spend this much money this month," Gordon said.

They believe their credit card account was hacked, and it may have taken place during their concert ticket transaction. Their statement showed that blocks of tickets were purchased from website likes Ticketmaster and StubHub, as well as major league baseball and football resale sites.

WISN 12 News has obtained court records that reveal email interactions that have helped federal officials unravel the suspects' business model, which is described as a full-service fraud ring. The group steals credit card numbers, scalps tickets, makes and sells fake tickets, and may even sell their lists of stolen account numbers.

When officials tracked the thieves' digital footprints to actual computers, it led them to some unexpected and very public locations: libraries.

Police records show that the crime ring has used Milwaukee County library branches as well as Brown Deer library computers to order thousands of dollars of tickets to Milwaukee Brewers games as well as concerts at the Riverside Theater and The Rave. Officials believe the crime ring has operated from southeast Wisconsin library computers since 2010.

The issue of scalped and fraudulent tickets not only affects the buyer, but the artists and venues as well.

"It's a major issue not just for us, but for the entire music business," said Andy Nelson of the Pabst Theater. He said their box office staff spends most of their time tracking black market online ticket sales.

"All that money is going to one guy somewhere," he said. "It's not going to the artist you love and it's not going to the music venue you're choosing to support."

The Thelins did not realize they were part of an international scheme until WISN 12 News contacted them. Gordon Thelin is a computer programmer, and said the case raises many questions.

"You could be watching them swipe (your credit card), but they could have a skimmer attached to the regular card reader," Thelin said. "That's reading all the information as it goes through. You wouldn't even know it."

Although investigators identified suspects in this crime ring early last year, no arrests have been made. Officials have subpoenaed library card records from the Milwaukee and Brown Deer libraries in an effort to help identify bogus ticket buyers.

Authorities said the best way for customers to protect themselves is to purchase tickets from reputable sources such as known ticket vendors and entertainment venues.

They also advise that if you make a credit card purchase through a site like Craigslist, keep a close watch on your credit card statements to ensure no unauthorized purchases have taken place.

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